I restarted Firefox in “safe mode” (i.e. unsafe mode-no plugins at all) with no difference. No popup, no combination of shift- or alt- or ctrl- plus clicking the reply icon does anything.
I can create a quote without the attribution by copy-n-paste text from a prior post, then manually set it to blockquote using the icon.
The quoting works for like like @Flatballer says.
That will work for me, just to give a context for my replies.